1. Field of the Invention
The present invention relates to a technique for inspecting a photo device.
2. Description of the Background Art
A photo device utilizes photovoltaic effect, and a photodiode, an image sensor, a solar cell and the like are manufactured as products, for example.
For example, solar cells utilizing single crystal silicon and polycrystal silicon occupy a mainstream, and studies are being conducted in order to enhance power generation efficiency. Moreover, the image sensor is being studied in order to increase sensitivity, to enhance an S/N ratio and to reduce a price with a focus on the security field or the sensing field.
The photo device is an element utilizing photoexcited carriers (a free electron and a free hole) generated by irradiating a depletion layer of a PN junction body with light. By analyzing a situation in which the photoexcited carriers are generated in the depletion layer of the photo device, therefore, it is possible to analyze a characteristic of the photo device. In the photo device, particularly, it is possible to enhance a performance of the photo device by increasing an absorption rate of the photoexcited carrier toward an electrode side. For this reason, it is demanded to analyze a process for disappearance of the photoexcited carrier in the photo device.
As one of methods of inspecting the photo device, it is known to utilize a luminous phenomenon. Specifically, when a voltage is applied to the photo device, thereby causing current to flow in a forward direction, an electron and a hole are bonded to each other in a PN junction part so that light (electroluminescent light) is generated. It is known that a defect of the PN junction part of the photo device is examined by utilizing the phenomenon (for example, International Publication No. WO2006/059615).
Moreover, an optical beam induced current (OBIC) method is known as an inspecting technique utilizing light. Specifically, a semiconductor on which an LSI or the like is formed is irradiated with a laser beam, and a photoexcited carrier thus generated is measured as current (Akihiko Ooi, “Technology of the Microscopic Analysis for Semiconductor Devices”, Fuji Jihou, Vol. 76, No. 3 (2003) pp. 197-200). The inspecting technique can also be applied to a photo device in addition to the semiconductor such as the LSI.
In the case of the inspecting method described in the Patent Literature 1, however, the electroluminescent light emitted from the photo device is feeble. For this reason, it is very hard to detect the process for disappearance of the photoexcited carrier in the depletion layer of the photo device.
Moreover, in the case of the inspecting method described in the Non-Patent Literature 1, a connection (wiring) for leading the photoexcited carrier generated in the depletion layer is required for measuring current. For this reason, it is necessary to cause a probe to come in contact with an electrode in the vicinity of the depletion layer in order to measure the photoexcited carrier with high precision. Accordingly, in the case in which the electrode is formed finely, it is hard to cause the probe to come in contact therewith. Moreover, in the case in which the probe is formed of a metal, the probe is caused to come in contact with the semiconductor so that there is a fear that the semiconductor might be damaged minutely or contaminated with a metal ion or the like. For this reason, there is demanded a technique for inspecting the photo device in non-contact as greatly as possible.